Process of preparing photoconductive poly-N-vinyl-carbazole type charge-transfer complexes

ABSTRACT

A process for preparing a charge-transfer complex with improved photoconductivity which comprises reacting poly-N-vinylcarbazole with tetranitro-9-fluorenone in a solvent of chlorinated hydrocarbon-ketone mixture in a 9:1 - 4:6 volume ratio.

Nukina et al.

PROCESS OF PREPARING PHOTOCONDUCTIVE POLY-N-VINYL-CARBAZOLE TYPE CHARGE-TRANSFER COMPLEXES Inventors: Kenji Nukina, Showa; Yoshi Arai, Oyama, both of Japan Assignees: Dainippun Ink & Chemicals Inc.,

Tokyo; Dainippun Ink Institute of Chemical Research, both of Japan Filed: June 10, 1974 Appl. No.: 478,054

Related U.S. Application Data Continuation of Ser. No. 260,191, June 6, 1972, abandoned.

Foreign Application Priority Data July 8, 1975 [56] References Cited UNITED STATES PATENTS 3,232,755 2/1966 Hoegl et a1. 96/l.5 X 3,484,237 12/1969 Shattuck 96/l.5

3,488,705 1/1970 Fox et al l 96/].6 3,512,966 5/1970 Shattuck et a] 96/16 X 3,661,879 5/1972 Van Dam et al. 96/15 X 3,697,264 10/1972 Poclbajny 96/].5 3,752,668 8/1973 Baltaui 96/1.5

Primary ExaminerNorman G. Torchin Assistant Examiner.lohn R. Miller Attorney, Agent, or F irmSherman and Shalloway [5 7] ABSTRACT A process for preparing a charge-transfer complex with improved photoconductivity which comprises reacting poly-N-vinylcarbazole with tetranitro-9- fluorenone in a solvent of chlorinated hydrocarbonketone mixture in a 9:1 4:6 volume ratio.

6 Claims, No Drawings PROCESS OF PREPARING PHOTOCONDUCTIVE POLY-N-VlNYL-CARBAZOLETYPE CHARGE-TRANSFER COMPLEXES This is a continuation of application: Ser. No. 260,191, filed June 6, 1972, now abandoned.

This invention relates to a process of preparing photoconductive poly-N-vinylcarbazole type chargetransfer complexes or a process of photosensitizing the N-vinyl-carbazole type polymers.

While numerous studies have been madeas to the use of the inorganic and organic substances as the photoconductive material in electrophotography, the inorganic substances, in view of their superiority in su ch respects as sensitivity and other points, have been put to practical use, those in use including, for example, selenium, zinc oxide and cadmium sulfide. While the organic substancesexcel in such points as flexibility, light transmittance and film-forming ability and also have the advantage of being light in weight, in view of their generally low sensitivity, the only substance that can be expected to become practically useful by its photosensitization is the N-vinyl-carbazole type polymer.

For this reason, numerous proposals have been made as to how to photosensitize the N-vinylcarbazole polymer. However, the conventional photosensitizing methods have the following shortcomings:

l. Adequate photosensitization cannot be achieved; Further, even though the photosensitization is achieved, the sensitivity achieved is lower than in the case of zinc oxide.

It is hypothesized that the photosensitization of the N-vinylcarbazole polymer has been made possible in the present invention, as hereinbefore described, for the following reason. That is, as a result of the discovery of the aforesaid chlorinated hydrocarbon-ketone mixture of a specified composition as being a solvent which can satisfactorily dissolve the tetranitro-9- fluorenone, a compound heretofore considered to be difficultly soluble, it has become possible to react the N-vinylcarbazole polymer with the tetranitro-9- fluorenone in a state wherein the latter is in solution in the solvent at a relatively high concentration, with the consequence that the tetranitro-9-fluorenone reacts with the N-vinylcarbazole polymer at a high rate to form the charge-transfer complex.

As the N-vinylcarbazole type polymers, in addition to the N-vinylcarbazole homopolymer, such copolymers as, for example, N-vinylcarbazole and such other monomers as vinyl acetate, vinyl chloride, acrylic compounds, etc. can be named method of the present invention can be applied to any of the N-vinylcarbazole 2. Since the dark current increases when the photosensitizer is cause to act on the polymer, the surface charge cannot be maintained for a prolonged period of time. That is, an image having a high contrast cannot be obtained. Y

3. The surface charge does not become zero even though it is exposed to light. That is, when a photoconchlorobenzene, etc., and a ketone such as acetone,

methyl ethyl ketone, acetophenone, acetonyl acetone,

.cyclohexanone, etc., mixed in a volume ratio of 9:1

ductive material of this sort is 'used in electrophotography, fogging of an image will take place.

An object of the present invention is therefore to prothe shortcomings such as noted-hereinabove.

Another object of the invention is to provide photosensitized poly-N-vinylcarbazole type which are of use as photoconductive materials.

Other objects and advantages of the invention will become apparent from the following description.

It has now been found that the N-vinylcarbazole polymers can be photosensitizedbyreactingthe N- vinylcarbazole polymer with tetranitro-9-fluorenone"in a solvent mixture consisting'ofachlorinated hydrocarbon and a ketone mixed in a volume ratio of 9:1 4:6, and preferably 8:2 5:5. The compound obtained by this reaction is a charge-transfer complex (molecular compound) formed on the basis-of the'transfer of electrons between the N-vinylcarbazole -polymei"(electron donor) and the tetranitro-9-fluorenone (electron acceptor). This charge-transfer complex has a sensitivity about 2 4 times that of zinc oxide, and the surface charge accepted from negative corona has a lesser tencompounds 4:6 is used as the reaction medium. When the chlorinated hydrocarbon is used at a rate exceeding this limit, the solubility of the tetranitro-9-fluorenone becomes poor, whereas when the amount of the chlorinated hydrocarbon used is below this limit, the solubility of the N-vinylcarbazole becomes poor. Thus, neither of these 'at the fore-going ratio and such that the N- transfer complex solution was applied to an aluminum vinylcarba-zole polymer is contained in the solvent mixture in the range of 2 15 weight and thereafter heating the solution for l lO'hours at a temperature ranging from 50C. to the reflux temperature.

The'invention will now' be more specifically illustrated by reference to the following non-limitative examples.

. EXAMPLES 1- XII- The N-vinylcarbazole polymer and tetranitro-9- fluorenone indicated in the following table were dissolved in the solvent indicated in the same table, after which the resulting solution was charged to a condenser-equipped flask and heated for 8 hours at the reflux temperature.

The so obtained poly-Nvinylcarbazole type chargeplate thereby preparing a photoconductive plate for electrophotographic use. This photoconductive plate potential and the potential after standing for 15 seconds were measured. The photoconductive plate was then exposed to light of 20 lux, and the time required acting 100 parts by weight of poly-N-vinylcarbazole with 30 220 parts by weight of tetranitro-9- fluorenone for a period of l to 10 hours at a temperature of from 50 to the reflux temperature in a solvent for the change to decrease to half and the time required 5 of a chlorinated hydrocarbon-ketone mixture having a for the charge to decrease to half and the time required 9:1 4:6 volume ratio, said poly-N-vinylcarbazole to become zero were measured. The value obtained by being used in an amount of 2 15% by weight based on multiplying the time required for the charge to dethe solvent. crease to half by the intensity of illumination is desig- 2. The process of claim 1 wherein said poly-N- nated sensitivity 1 and the value obtained by multiply- 10 vinylcarbazole is a copolymer composed of at least ing the time for the charge to become zero by the lnten- 60% by weight of N-vmylcarbazole and at most 40% by sity of illumination is deslgnated sensitivity ll. Both weight of vinyl acetate. these values are shown in the following table. 3. The process of claim 1 wherein said poly-N- Example N-vinylcarbazole Tetranitro-9- Solvent Initial Potential Sensitivity type polymer fluorenone potential minutes (Lux-Sec) (V) later (V) I ll l poly-N-vinyl- 2,4,5 ,7-tetranitrodichloromethane 310 254 22 272 (control) carbazole* 9-fluorenone (10.0 g) (2.0 g) (100 cc) ll N-vinylcarbazoledo. (2.5 g) chlorobenzene 360 334 16 280 (control) vinyl acetate (100 cc) copolymer" (10.0 g) 111 do.** (10.0 g) do. (3.0 g) chlorobenzene 440 400 12 190 (90 cc) acetone (10 cc) N do.** (10.0 g) do. (4.0 g) chlorobenzene 420 380 7 75 (80 cc) acetone (20 cc) V do. (10.0 g) do. (5.0 g) chlorobenzene 420 370 6 72 (70 cc) acetone cc) V1 do.** (10.0 g) do. (6.0 g) chlorobenzene 400 370 5 7O cc) acetone (40 cc) Vll do.** (7.0 g) do. (4.0 g) 1.2-dichloro- 500 420 8 80 do.***(3.0 g) ethane cc) acetone (30 cc) Vlll poly-N-vinyl- 2,3,6,7-tetranitro- 1,2-dichloro- 300 246 6 carbazole* 9-fluorenone ethane (70 cc) (10.0 g) acetone (30 cc) IX N-vinylcarbazole- 2,4,5,7-tetranitrochlorobenzene 480 440 8 85 vinyl acetate 9-fluorenone cc) copolymer**** (4.0 g) acetophenone 10.0 g) (20cc) X do.****( 10.0g) do. (5.0 g) chlorobenzene 480 430 7 75 cyclohexanone (30 cc) Xl do. (10.0 g) 2,3,6,7-tetranitrochlorobenzene 470 450 9 9-lluorenone (50 cc) (4.0 g) methyl ethyl ketone (50 cc) Xll do. (5.0 g) 2,4,5,7-tetranitrochlorobenzene 415 395 5 68 9-fluorenone cc) "LUVICAN M-l70, a product of Badische Anilin-und Sodafabrick A.G.

acetone (60 cc) "A copolymer of N-vinylcarbazole and vinyl acetate in a weight ratio of 80:20 (Intrinsic viscosity as measured in benzol 3 X 10 "A copolymer of N-vinylcarbazole and vinyl acetate in a weight ratio of 60:40 (Intrinsic viscosity as measured in benzol 3 X 10 ""A copolymer of N-vinylcarbazole and vinyl acetate in a weight ratio of 70:30 (lntrinsic viscosity as measured in benzol 3 X 10).

From the data shown in the foregoing table it can be appreciated that by the use of the poly-N- vinylcarbazole type charge-transfer complex of the present invention as the photoconductive material a photoconductive film coating is formed, which demonstrates excellent sensitivity, as well as in which the tendency to attenuation of the surface charge by means of the dark current is checked and also in which the surface charge becomes zero in a relatively short period of time on exposure to light.

We claim:

1. A process of preparing a charge-transfer complex with improved photoconductivity which comprises renone. 

1. A PROCESS OF PEPARING A CHARGE-TRANSFER COMPLEX WITH IMPROVED PHOTOCONDUCTIVITY WHICH COMPRISES REACTING 100 PARTS BY WEIGHT OF POLY-N-VINYLCARBAZOLE WITH 30 - 220 PARTS BY WEIGHT OF TETRANITRO-9-FLUORENONE FOR A PERIOD OF 1 TO 10 HOURS AT A TEMPRATURE OF FROM 50* TO THE REFLUX TEMPERATURE IN A SOLVENT OF A CHLORINATED HYDROCARBON-KETONE MIXTURE HAVING A 9:1 - 4:6 VOLUME RATIO, SAID POLY-N-VINYLCARBAZOLE BEING USED IN AN AMOUNT OF 2 - 15% BY WEIGHT BASED ON THE SOLVENT.
 2. The process of claim 1 wherein said poly-N-vinylcarbazole is a copolymer composed of at least 60% by weight of N-vinylcarbazole and at most 40% by weight of vinyl acetate.
 3. The process of claim 1 wherein said poly-N-vinylcarbazole is a homopolymer of N-vinylcarbazole.
 4. The process of claim 1 wherein said tetranitro-9-fluorenone is 2,4,5,7-tetranitro-9-fluorenone.
 5. The process according to claim 1 wherein said tetranitro-9-fluorenone is 2,3,6,7-tetranitro-fluorenone.
 6. The process of claim 1 wherein said chlorinated hydrocarbon is selected from the group consisting of chlorobenzene and 1,2-dichloroethane, and said ketone is selected from the group consisting of acetone, methyl ethyl ketone, acetophenone and cyclohexanone. 